There are three main sources of polluting gasses from an internal combustion engine: engine exhaust, crankcase, fuel supply systems. In the fuel tank, the hydrocarbons that are continually evaporating from the fuel constitute a significant contributing factor to air pollution.
To control the air pollution resulting from these emissions, governments establish quality standards and perform inspections to ensure that standards are met. Standards have become progressively more stringent, and the equipment necessary to meet them has become more complex. Emissions from the fuel tank are reduced by an evaporated fuel processing device, the heart of which is an evaporative canister of activated carbon capable of holding fuel vapour. In operation, the fuel tank vapours flow from the fuel tank to a liquid-vapour separator that returns the raw fuel to the tank and channels the fuel vapour to the canister. The evaporative canister acts as a storehouse; when the engine is running, the vapours are purged from the evaporative canister through the purge port into the combustion chamber, where they are burnt.
An evaporative canister is e.g. known from US patent application US-A-2002/0007826. The evaporative canister is a typically vertical-placed type integrated canister connected to a fuel tank. Evaporated fuel from the fuel tank is led to the evaporative canister via an evaporated fuel passage and, optionally, a liquid-vapour separator. The latter traps the fuel in a liquid phase. The fuel in the vapour phase only is fed into the canister via a tank port. The air/fuel vapour mixture first flows through a first adsorbent chamber comprising an adsorbent material and then through a second adsorbent chamber also comprising an adsorbent material. As the air/fuel vapour mixture flows through the first and second adsorbent chambers, the fuel component of the mixture is adsorbed by the adsorbent material and purified air exits the canister via an atmospheric port. During operation of the engine, air is drawn through the canister from the atmospheric port, through the second and first adsorbent chambers, and out via a purge port. As the air passes through the second and first adsorbent chambers the air desorbs the fuel component from the adsorbent material, whereby the latter is regenerated. The purge port is connected to the internal combustion engine, where the fuel component is then burnt.
Such evaporative canisters are however not designed to meet new, stricter regulations on fuel evaporating from vehicles.